It has been well known that lactic acid bacteria are distributed as normal bacterial floras (enteric bacilli) in intestinal tracts and cavities of human beings or animals and are useful for maintaining their health. Recently, remarkable progress in study of intestinal micro-floras (hereinafter may be referred to as "floras") has gradually revealed a role of lactic acid bacteria.
In this connection, attention is drawn to the effects of lactic acid bacteria preparations and various kinds of food including lactic acid bacteria, such as fermented milk and sour milk beverage.
Generally speaking, such intestinal floras comprise a group of lactic acid bacteria, an anaerobic group, and an aerobic group.
These intestinal floras comprise useful bacteria, such as lactic acid bacteria, which are useful to human beings and animals, and harmful bacteria which are harmful to the contrary. Such useful and harmful bacteria both live in intestines with a specific balance kept therebetween.
Herein, the term "useful bacteria" indicates those bacteria which are useful to maintain the health of a host by various activities, for example, synthesis of vitamin and protein, promotion of digestion and absorption, suppression of proliferation of foreign bacteria, stimulation of immune functions, or the like. On the other hand, the term "harmful bacteria" indicates those bacteria which produce in intenstines various materials that are harmful to the host and are therefore considered to relate to the causes of various acute or chronic diseases, senility, and cancer.
Accordingly, it is understood that human diseases, senility, and cancer can be avoided and human being can stay being healthy, if harmful bacteria in intestines are suppressed and useful bacteria are increased to the contrary.
As regards livestock, it has been well known that administration of useful bacteria, such as lactic acid bacteria, or fermented products thereof is effective in promoting growth and in preventing and curing diseases such as diarrhea. Recently, such application has been widely made.
These preparations are called probiotics and has become into worldwide use.
In the meanwhile, infant animals are inherently germ-free when they are born. As soon as they are born, various bacteria begin enter into their bodies environment.
The balance between useful bacteria and harmful bacteria in intestinal floras of infant animals gradually become stable with the lapse of days after birth. However, the balance is often affected by environment and change of feed.
Specifically, in infant animals, useful bacteria are liable to decrease while opportunistic Escherichia coli is liable to profiferate rapidly.
Proliferation of opportunistic Escherichia coli breaks the balance in intestinal floras to often cause diseases.
If viable cell preparations such as lactic acid bacteria preparations are preventively administered to infant animals, the acidity of their intestines can be maintained. In this event, proliferation of Escherichia coli is suppressed so as to effectively prevent various diseases resulting from imbalance in intestinal floras.
Administration of such viable cell preparations generally has a remarkable effect on infant animals. If applied to healthy adult animals, a considerable effect is also observed.
Intestinal floras of adult animals maintain a delicate balance which is not always constant. The balance is easily broken due to stimulation by environment, such as stress.
Specifically, the balance in intestinal floras is highly dependent on a pH in intestines.
If lactic acid bacteria are predominant and produce lactic acid sufficiently, the acidity in intestines is maintained so as to suppress proliferation of Escherichia coli.
On the contrary, when the activity of lactic acid bacteria is diminished, organic acid such as lactic acid is reduced. In this event, Escherichia coli readily proliferates to thereby cause diseases such as diarrhea.
For viable cell preparations, use may be made of intestinal bacteria derivatives or other bacteria that are not belong to normal intestinal bacteria. Intestinal bacteria derivatives which can proliferate in intestines of animals dosed are desirable.
However, some intestinal bacteria cannot colonize in intestines of animals of different species because of specific characteristics.
In other words, even if particular intestinal bacteria are inherent to a particular animal, they are liable to be eliminated by indigenous bacteria in case when they are administered from outside. It is to be noted that colonization and proliferation in intestines would not always be expected.
Accordingly, if further administration of bacteria is stopped, the bacteria that have already been supplied disappear from intestines in a relatively short period of time.
It is reported that, even in such case, continuous administration of more than a predetermined amount of viable cell preparations is effective in preventing and curing diarrhea and in promoting growth, irrespective of colonization. This is because the administered bacteria themselves act in intestines or aid to maintain and proliferate useful bacteria that have indigenously existed in intestines.
Generally, in order to improve efficiency of viable cell preparations, a necessary amount of viable cells must reach intestines through a stomach.
Therefore, essential properties required to the bacteria are: to be stable in preparations; to be stable in feed or drinking water into which the preparations are mixed; to be acid-resistant in a stomach that shows high acidity among other digestive tracts; and to be resistant to sterilizing action of bile in small intestines.
In addition, recent and strong demand exists for viable cell preparations in that viable cells have high activity to perform intestinal action with high efficiency.
Desirably, viable cells sufficiently proliferate so as to colonize in intestines. It is at least necessary for viable cells to be highly effective in promoting proliferation of indigenous lactic acid bacteria.
Such viable cell preparations must have a high survival stability of bacteria in the preparations. In addition, the viable cell preparations must reach inside of intestines against severe conditions in digestive tracts.
Even though many viable cell preparations are commercially available at present, no preparations sufficiently meets these requirements.
It is an object of the present invention to find a lactic acid bacteria strain satisfying the requirements for viable cell preparations and to provide lactic acid bacteria preparations having a sufficient survival stability and satisfying various requirements, and a manufacturing process of the preparations.